An air-fuel ratio of an engine may be varied rich and lean of stoichiometric conditions to improve efficiency of a three-way catalyst located in the engine's exhaust passage. The engine air-fuel ratio is often varied at a predetermined frequency and amplitude. Operating the engine rich provides hydrocarbons and CO to the three-way catalyst for reducing exhaust gas constituents such as NOx. Conversely, operating the engine lean provides oxygen to the three-way catalyst for oxidizing hydrocarbons and CO. However, operating an engine rich of stoichiometry may increase engine output torque while operating the engine lean of stoichiometry may decrease engine output torque. Consequently, varying the engine air-fuel ratio may disturb torque transmitted by the engine to the driveline, and a driver of the vehicle may find the torque disturbances objectionable.
The inventors herein have recognized the above-mentioned disadvantages and have developed a method for operating a driveline, comprising: varying an engine air-fuel ratio; and adjusting torque of a motor supplying torque to the driveline in response to varying the engine air-fuel ratio.
By adjusting torque supplied by a motor to a driveline when engine torque is varying due to engine air-fuel ratio changes, it may be possible to smooth engine torque so that the technical results of increasing catalyst efficiency and decreasing driveline torque oscillations may be provided. Further, if a battery state of charge (SOC) is less than a threshold level for a battery supplying power to the motor, the possibility of producing driveline torque oscillations may be reduced via adjusting engine spark timing in response to the engine air-fuel ratio.
The present description may provide several advantages. In particular, the approach may reduce driveline torque disturbances of a hybrid driveline. Further, the approach may improve vehicle drivability. Further still, the approach may reduce driveline wear, thereby increasing the operating life of the driveline.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.